Generally, high-temperature heat is generated within a containment building of a nuclear power plant by a severe accident due to direct heat, design basis events, or a loss accident of an air cooling apparatus, etc. The high heat generated directly or indirectly affects the inside of the containment vessel as well as the instrument circuit. A physical change in the instrument circuit due to these accidents makes an open circuit, a ground circuit, or a short circuit, and the like, an extreme state going through an incomplete transition state, wherein error information can be input due to an abnormal signal in a transient state exceeding instrument environmental conditions and design range and judgment errors can be caused due to the error information.
Therefore, a need exists for analysis methods and analysis apparatuses capable of quantitatively analyzing the causes of the failure circuits from the error information through a transient signal analysis technology, under a degradation condition in circuit elements due to the physical change in the instrument caused by the high-temperature environment that is the severe accident affecting the nuclear power plant.
A need is raised to establish an instrument survivability assessment and schemes capable of measuring severe accidents with respect to defective instruments, according to SECY 89-012 “Staff plan for accident management regulatory and research programs” request procedure enacted after a “Three Mile Island” accident together with the aforementioned problems. However, what is proposed as the scheme for measure the accidents until now applies a simple function of PSpice. This is only a research result of Electric Power Research Institute (EPRI) (USA) that describes an error validation (point or range) for the equivalent circuits of some instruments according to the environmental conditions and suggests only problems of matters described in this report.
Since an improvement of safety technology due to an increased operational rate of a nuclear power plant has been raised as an important problem in a field of nuclear power generation, assessment methods and apparatuses with high accuracy meeting an instrument survivability assessment, which is one of important elements of accident management plan, are urgently needed. In particular, in order to maximally use the assessment method or the assessment apparatus, it is to be able to perform a quantitative analysis such as a simulation experiment, reconstruction with respect to an abnormal condition, etc., as well as a qualitative analysis such as a decision on whether there is an error in an actual situation. Also, in order to maximally use the assessment apparatus, a field worker is to be able to conveniently use the assessment apparatus by easily connecting it to the instrument.